Flexible contact lenses are well known to the art. There are a number of basic types of these lenses. One of the oldest of these is made from a base material of crosslinked hydroxyethylmethacrylate. This material achieves its flexibility by inflation or absorption of a substantial amount of water, frequency 35 to 75% by weight of the base material. Because of their structure the above acrylate materials are frequently sensitive to the pH of the lachrymal fluid, can tear easily and due to their requisite highly hydrophilic structure are subject to biological contamination which is then difficult to eliminate. A second type of lens made of a specified silicone polymer has been described in U.S. Pat. No. 3,228,741. Silicone polymers of this type are primarily lipophilic and have well known hydrophobic characteristics. In addition, they generally require an incorporated inorganic filler, such as silica, to provide enough material strength to make their use practical. Because of the use of a filler it is difficult to obtain a proper index of refraction in the material to facilitate fabrication of lenses suitable for correction of astigmatism. The lack of hydrophilicity and consequent non-wettability of the surface of silicone lenses leads to rupture of the tear of lachrymal fluid film. Such film tearing results in irritation and reduction in the amount of time the lens can be safely and comfortably worn. The problem of surface wettability of silicone type lenses has been considered in U.S. Pat. No. 3,700,573 assigned to the assignee hereof. The approach taken in this patent was an attempt to render the silicone polymer hydrophilic by grafting it with polyvinylpyrrolidone. While this graft method has merit, it has not been completely satisfactory because of the enormous individual variation of the lacrymal film. The cornea is a living tissue and as such must be protected from abrasion to avoid irritation and possible permanent damage. The cornea normally produces a fluid which covers it and thus reduces any abrasion between it and objects, such as a contact lens, placed upon it. This fluid layer can be considered as a pre-corneal film and therefore in addition to its anti-abrasion function, it must be kept in a continuous non-ruptured state for proper distortionless vision. This fluid layer or lachrymal film performs numerous other functions in relation to the cornea such as waste disposal, oxygen transport, electrolyte balance and the like. This functional multiplicity results in the film being entirely dependent on the individual. The percentage composition of aqueous and lipidic components in the film thus also varies with the individual.
It is thus understood that a contact lens having hydrophilic and lipophobic properties, to prevent tear film rupture in the greatest proportion of individuals is extremely desirable. Provision of such a lens would increase the amount of time the lens could be worn, reduce eye irritation and provide better vision because of elimination or substantial reduction of any distortion caused by rupture of the film.